A boat downstream in 3 hours covers the same distance as in 4.5 hours upstream.

A boat downstream in 3 hours covers the same distance as in 4.5 hours upstream. Calculate the boat’s own speed if the current speed is 3 km / h.

Let the boat’s own speed be x km / h. Then the speed of the boat along the river will be equal to (x + 3) km / h, and against its course – (x – 3) km / h. Based on this, as well as the conditions of the problem, we compose an equation and solve it:

(x – 3) * 4.5 = (x + 3) * 3,

4.5x – 13.5 = 3x + 9,

4.5x – 3x = 9 + 13.5,

1.5x = 22.5,

x = 22.5 / 1.5,

x = 15 km / h.

This is the proper speed of the boat we are looking for.

Answer: the boat’s own speed is 15 kilometers per hour.